You say that you have given him repeated warnings. But then were these verbal warnings or written ones? If these were written warnings, have you issued a hard copy to the employee and maintained its office copy? If yes, then based on the evidence, you may issue a show cause notice asking him to explain why administrative action should not be initiated against him for his under-performance. If the reply is not satisfactory, you may order a domestic enquiry. In the enquiry, give the employee a chance to defend his position. If the under-performance is proved then you may take disciplinary action against him which could be either demotion or termination.
If the employee is demoted then you may reduce his designation, you may reduce his salary also but while reducing salary, make sure that basic pay is maintained at the same level.
5th September 2018 From India, Bangalore
Suggestion of making debit note for his mistakes was also proposed to Management instead of pay decrease, it was not accepted as the prime complaint against him is time wastage and need regular supervision in his work which is insubstantial.
5th September 2018 From India, New Delhi